1. Field of the Invention
The present invention relates generally to the field of data communication receivers, and more particularly to a data communication receiver having variable length message carry-on.
2. Description of the Prior Art
There are many data communications systems in operation today which provide message distribution to data communication receivers, such as pagers. Many of these system utilize signaling protocols which utilize time slots, or transmission frames, to which the pagers are assigned, thereby providing a battery saving function during the normal course of message transmission. A paging terminal was provided in such systems to encode the received messages for transmission to the intended pagers during the assigned transmission frames. In signaling protocols such as the POCSAG signaling protocol, each time slot, or transmission frame, allowed for the transmission of only two code words, either both address code words, an address and a message code word, or two message code words. Since the transmission of even a simple telephone number required as a minimum two message code words, numeric message transmissions required on the average one and one-half frames, which periodically resulted in the inability to transmit address code words during the assigned transmission frames, because the transmission frame was filled by message code words associated with address code words transmitted in the previous transmission frame.
The above problem was alleviated in some signaling protocols by increasing the number of code words which could be transmitted in any transmission frame. However, when the number of transmittable code words is selected for the transmission frames, such transmission frames often have to be filled with idle code words when an insufficient number of messages have been received for transmission during any particular transmission frame. Such signaling protocols were also limited in the number of data communication receivers, or pagers, which could be assigned, or operated on any given channel, before the channel reached its maximum capacity. By increasing the transmission speed, additional pagers could be added to the system, however at the expense of a significant amount of unused channel capacity, until the system again filled up. There is a need to be able to provide a flexible system which enables reconfiguring the amount of information which can be transmitted on the channel within the available transmission frames in order to maximize message throughput on the channel.